Common working machines having both a working part and a transporting part driven by an engine appear for example in JP-A-1-163304 and JP-UM-A-3-32617.
However, there are working machines in which the drive sources of the working part and the transporting part are separate. For example working machines having a working part driven by an engine and a transporting part driven by an electric motor appear in JP-B-53-5210 and JP-A-2001-271317. If the working part is drive-controlled with an electric motor like this, there is the advantage that the working machine can be made more maneuverable.
As an example of a working machine having the drive sources of its working part and its transporting part separate, the working machine disclosed in JP-A-2001-271317 will now be described in outline on the basis of FIG. 15.
Referring to FIG. 15, this working machine 200 has on a machine body 201 a working part 204 made up of an auger 202 and a blower 203; an engine 205 for driving the working part 204; left and right transporting parts 206, 206 consisting of crawlers; left and right electric motors 207, 207 for driving these transporting parts 206, 206; a generator 209, driven by the engine 205, for supplying electrical power to a battery 208 and the electric motors 207, 207; and a control part 211 for controlling the electric motors 207, 207.
The generator 209 is driven with part of the output of the engine 205, and the electrical power obtained is supplied to the battery 208 and the left and right electric motors 207, 207. The remainder of the output of the engine 205 is allocated to driving the working part 204 via an electromagnetic clutch 212. Thus, the working machine 200 is a snow-remover of a type in which a working part 204 is driven by an engine 205 and transporting parts 206, 206 are driven by electric motors 207, 207.
Now, when the working machine 200 is only being made to move along, because all that is happening is that the transporting parts 206, 206 are being driven by the electric motors 207, 207, the load on the engine 205 is small. And even during snow-removing work with the working machine 200 traveling, when the height of the accumulated snow is low or when the snow is light in quality, the load on the engine 205 is small. In the case of a light load like this, to reduce fuel consumption and have consideration for the working environment, it is desirable to reduce the engine speed by lowering the throttle aperture.
However, during snow-removal work, the size of the load often fluctuates. For example, to deal with the light load of just making the working machine 200 travel, the engine speed is lowered to a so-called low idle state. When from this state the working part 204 is driven and snow-removing is carried out, because a working load is added to the transporting load, even if it is only a light working load, the load on the engine 205 increases. Because the engine speed falls in correspondence with this increase in load, the speed of the electric motors 207, 207 also falls. As a result, the travel speed of the working machine 200 falls and the efficiency of the snow-removal work decreases. To maintain work efficiency, it is necessary for the operator to increase the engine speed by adjusting the throttle aperture.
When it is necessary to adjust the throttle aperture like this every time the load fluctuates, controlling the working machine 200 is troublesome. On the other hand, if the throttle aperture is constantly set high to reduce the trouble of control, energy is wasted and this is therefore undesirable.
Accordingly, a working machine has been awaited with which it is possible to make control of the working machine simpler by improving the operability of the working machine and reducing the frequency with which it is necessary to adjust the throttle aperture of the engine.